If you’ve ever taken an SSRI that makes you want to go out and start living life again, you may be able to relate to crayfish. A study published Wednesday in Ecosphere inspects the effects of selective serotonin reuptake inhibitors, or SSRIs, on crayfish, finding that the medication that helps people with depression actually makes crayfish act more “boldly” when added in small amounts to their environment.
There are trace amounts of many pharmaceuticals in bodies of water around the world, thanks to how humans metabolize our medicines and dispose of wastewater. “When you take a medication, nobody’s body is 100% efficient, so when we take a pill, we might only metabolize and actually use 90%, or 80%, or 70%,” said AJ Reisinger, an assistant professor at the University of Florida’s Soil and Water Sciences Department and lead author of the study. “Whatever is left over and not used by our body will be excreted directly into our toilets, flushed, then through a sewer and into a wastewater treatment plant—or, if the sewer line is leaking, directly into our groundwater.”
Most pharmaceuticals in our water stay at pretty low levels; Reisinger said there’s been lots of previous work on the concentration of drugs needed to kill plants and animals, which is a lot higher than the concentration we see in the environment. “People are often not concerned [about pharmaceuticals in the water] because of that,” Reisinger said. But there’s an emerging body of work that studies how these low concentrations can change behavior and interactions among animals and plants, including altering photosynthesis rates, changing the life cycles of insects, and other effects.
SSRIs like Zoloft and Prozac are some of the most commonly prescribed medications in the United States right now: one survey found that SSRI use skyrocketed 64% between 1999 and 2014, while almost 20% of U.S. adults took antidepressants in 2017. “If everybody is taking medication, those small amounts can add up a little bit” in the water, /Reisinger said. He added that some previous work with crayfish, which are a crucial species in the aquatic food chain, found that injecting them directly with serotonin made them more aggressive. Since SSRIs work to make serotonin more available to the brain, testing how SSRI levels in the water affect crayfish was an interesting question for researchers.
To figure out how these medications in the water affect crayfish, researchers recreated a crayfish’s natural habitat: an artificial stream, complete with leaves and rocks that had been left in real streams for a few weeks. Into some of these streams, they piped an “environmentally realistic concentration” of SSRI.
After two weeks of letting the crayfish settle in (and letting some of them absorb that sweet, sweet antidepressant water), researchers performed a behavioral experiment: they constructed a Y-shaped plexiglass maze, with one branch of the Y filled with chemicals that signaled food and the other filled with chemicals to signal the presence of another crayfish. They placed the crayfish’s shelter at the bottom of the Y and watched the animals as they emerged and chose which Y arms to explore. The researchers observed that the crayfish exposed to antidepressants came out of their shelters earlier on average than the control group. The antidepressant-exposed crayfish spent most of their time in the Y arm with the food chemicals, not the arm with the signs of the other crayfish, suggesting that their aggression levels weren’t raised as they got braver. The findings are similar to studies done on the effect of Prozac on crabs, which found that the drug made crabs a whole lot braver.
Anyone who’s been in a depression hole for weeks or months, where you can’t muster up the will to leave your bedroom, knows that SSRIs helping you to more boldly enter the world is generally a good thing. But for the crayfish, it’s a little more complicated. The drugs could prod them to get out and eat more food—but the world they’re entering is a lot more dangerous for them than it is for us, full of predators that could take the opportunity to snack on a crayfish feeling more emboldened than usual to leave its shelter.
“I understand anthropomorphizing these things, and I don’t want to say it’s a good or a bad thing, because it’s just nature, and nature is responding,” Reisinger said. “It’s a high-risk, high-reward response that they’re doing.”
There’s a whole lot more research that needs to be done on various species’ responses to different drugs. But Reisinger said he hopes this study first raises awareness of what exactly is in our water.
“It’s not just super-polluted systems—we find pharmaceuticals and a lot of other synthetic chemicals in a lot of different ecosystems,” he said. “Just because they’re really low concentrations doesn’t mean they’re not an ecological threat or not having an impact. We already know freshwater bodies are threatened by a ton of different things, so this is just another thing that’s going on in our water bodies.”